The present invention relates to improved techniques for displaying video images transmitted over a computer network. More particularly, the present invention relates to improved methods and apparatus for implementing control features, such as play, rewind, fast forward, pause, stop, record, and the like, on a real-time video stream and/or live video stream delivered via a computer network from server computers to client computers.
It is well known that digital video data may be manipulated and rendered using computers. In a computer network, e.g., a client-server computer network, one or more computers may be employed to receive the analog video data (e.g., from a video camera), encode that analog video data to a suitable digital format, and store the digital video data file. Using a computer coupled to the network, a user may, at a subsequent time, request the pre-stored digital video data file for display on a video display associated with the client computer.
As computers become more pervasive in the workplace and in the home, the demand for digital video services correspondingly increases. By way of example, it has been recognized that it is possible to employ networked computers as a mass communication medium whereby a pre-stored digital video file may be transmitted from a server to one or more client computers to permit the client computers to display the images after the file is received. This technology may be employed to, for example, deliver movie or training video clips from a central server to one or more client computers for display.
In the above example, it is typically necessary for the client computer to receive the entire pre-stored digital video file prior to rendering the images. Real-time video streaming, on the other hand, refers to the situation wherein the client computer renders the images while they are streamed from the server computer. In some applications, real-time video streaming is favored since it permits the user to begin viewing video frames shortly after requesting the video file instead of having to wait until the entire pre-stored file is downloaded from the server computer.
It has been found, however, that real-time video streaming is difficult to implement on heterogeneous, lossy networks such as corporate intranets or the Internet, i.e., the well-known international computer network that links, among others, various military, governmental, educational, nonprofit, industrial and financial institutions, commercial enterprises, and individuals. This is because real-time digital video applications, as are all digital video applications, are resource-intensive to implement. Even with compression, the transmission of quality video clips (i.e., those with acceptable frame rate and frame quality) places a heavy bandwidth burden on the computer network. For that reason, real-time video streaming has traditionally been implemented on proprietary and expensive networks that are capable of supporting a high bit rate (e.g., private high-speed local area networks (LAN) or dedicated data links).
Furthermore, real-time video data is time-sensitive, i.e., the data packets containing the real-time video data must be received in a timely manner in the proper sequence for acceptable display. In bandwidth limited networks, e.g., corporate intranets which support a high number of users or heterogeneous, lossy public networks such as the aforementioned Internet, the time-sensitive nature of real-time digital video data poses special challenges. There is, for example, less time to retransmit a lost data packet because if the time for displaying a given data packet at the client computer has passed, there is little use for that data packet if and when it arrives.
It has also been found that real-time digital video streaming poses complex frame synchronization issues. Since the video frames to be displayed are not stored with the client computer, there is no pre-stored file on which to perform control features such as rewind, fast forward, play, and pause. Typically, the video frames necessary for performing these functions are requested from the server computer itself. Responsive to the control commands, the video frames necessary for performing the requested control feature are then streamed to the client computer, typically over the same data connection to minimize the latency associated with opening another data connection. As can be appreciated by those skilled, complications can arise while switching among different groups of video frames, some of which may be waiting to be sent at the server, waiting to be displayed at the client, in transit through the network, or lost.
The complexity involved in implementing control features on real-time video stream is further compounded by the requirement of low latency, which is imposed by real-time video applications, i.e., the requirement that any delay between the time a given video frame is transmitted from the server computer and the moment it is rendered at the client computer be minimized. Unless these control features are properly implemented, undue latency may occur and/or the quality of the viewing experience may degrade.
All the challenges discussed above also apply to live video streaming. In live video streaming, the video data may be digitized in one location, then encoded and transmitted to a client computer (via a server) substantially instantaneously (with some delay due to the encoding and transmission of video frames) for display. Live video and real-time video may be thought of as subsets of streamed video since both live video frames and real-time video frames are rendered as they are streamed from the server. Live video rendering, however, results in the display of most recently encoded video frames whereas real-time video rendering may result in displaying past video frames of a currently recorded event or even an event that happened and was recorded a long time ago. As can be appreciated, live video streaming applications are even more sensitive with respect to the data packets transmitted via the network. This is because the live event being record continues to unfold, and video frames related thereto continue to be formed and require to be displayed as time goes by.
Frame synchronization issues pertaining to live video streaming are further complicated by the fact that the digital video data file at the server is being formed at the same time the video frames pertaining thereto are displayed at the client computer. This is because copies of video frames sent to the client computer are also stored in the server in a digital video data file for subsequent use. Accordingly, there are complexities involved when, for example, the user wishes to switch from a live video viewing mode to a rewind mode, view past video frames for a few seconds, and fast forward to the end of the still growing digital video data file to again play live video frames. Because of the complexities involved, as well as the bandwidth and latency requirements, prior art attempts at implementing control features on live video streams have largely been unsatisfactory. While this is true for most networks, it is particularly true for the Internet wherein the transport network is typically lossy and outside the control of the owner of the server and/or the client computer, and wherein the bandwidth available is both limited and subject to fluctuations.
In view of the foregoing, there are desired improved methods and apparatus for implementing control features on real-time video streams and/or live video streams transmitted via a computer network from server computer(s) to client computer(s).